1. Field of the Invention
The present invention relates to a workpiece carrier apparatus for transfer press machine to carry workpiece to a press station, and to hold workpiece pressed and processed at one press station, and carry it to the next press station for sequential press forming.
2. Description of the Related Art
A transfer press machine conducts press operations while carrying workpiece press formed at various press stations to the next press station in sequence, and synchronized with the raising and lowering operation of an upper die. The transfer press machine incorporates a workpiece carrier apparatus. The workpiece carrier apparatus incorporates a cross bar fitted with a workpiece holder which operates between adjacent press stations in an approximately rectangular movement to constitute a carrier motion. Workpiece press formed at an upstream press station is gripped in the workpiece holder and lifted, carried to the next downstream press station, and then lowered and moved onto the lower die of the press station.
A variety of mechanisms are used for the workpiece carrier apparatus for transfer press machine. In the majority, carriers incorporating a cross bar and are installed at each press station perform feed operation and raising and lowering operation.
FIG. 9 shows one example in outline. Press stations 6 for forming the workpiece with a press die comprising a lower die 3 installed via a bolster 2, and an upper die 5 placed such as to be capable of being raised and lowered by a slide 4 above the lower die 3, are arranged apart at required spacing at multiple locations along a press line L on a bed 1 installed along the press line L. Furthermore, on both sides of the press line L is arranged a pair of left and right lifting beams 7, parallel with the direction of the press line L, and symmetrical with the press line L therebetween, each of the left and right lifting beams 7 being capable of movement in the vertical direction (raised and lowered) via a rack and pinion mechanism 9 driven by an AC servo motor 8 mounted above. Moreover, multiple carriers 10 arranged to match the spacing of the press stations 6 are installed on each of the left and right lifting beams 7 such as to be able to run along the press line L, and cross bars 11 extending at right angles to the direction of the press line L and fitted with workpiece holders 12 are arranged between the carriers 10 opposed in the left-right direction, and both ends of the cross bars 11 are supported by the left and right carriers 10. On the other hand, adjacent carriers 10 in the direction of the press line L are connected via connecting rods 13, and a rack and pinion mechanism 15 fitted with an AC servo motor 14 is connected to the carrier 10 on one end in the direction of the press line L via a connecting rod 16. As described above, the carriers 10 and cross bars 11 fitted with the workpiece holders 12 are capable of being moved vertically by the raising and lowering of the lifting beam 7 driven by the AC servo motor 8. Moreover, movement of all carriers 10 in synchronization in the direction of the press line L via the rack and pinion mechanism 15 driven by the AC servo motor 14 and the connecting rods 16 and 13, allows movement of the cross bars 11 fitted with the workpiece holders 12, in the direction of the press line L (see for example, Japanese Unexamined Patent Application, First Publication No. Hei 10-328766).
In practice, with the conventional workpiece carrier apparatus for transfer press machine described above, the cross bars 11 are supported on each carrier 10 fitted to the lifting beam 7, and movement of each cross bar 11 vertically and in the direction of the press line L is all simultaneous and uniform. Therefore, the workpiece cannot be carried with a different motion at each press station 6. Hence, only the same operation is possible for the workpiece carrying motion (interference curve) at each press station, thus restricting die shape in order to avoid interference, and resulting in problems in forming of a diverse range of workpiece.